Moons of Jupiter - Discovery

Discovery

The first claimed observation of one of Jupiter's moons is that of the Chinese astronomer Gan De around 364 BC. However, the first certain observations of Jupiter's satellites were those of Galileo Galilei in 1609. By March 1610, he had sighted the four massive Galilean moons with his 30x magnification telescope: Ganymede, Callisto, Io, and Europa. No additional satellites were discovered until E.E. Barnard observed Amalthea in 1892. With the aid of telescopic photography, further discoveries followed quickly over the course of the twentieth century. Himalia was discovered in 1904, Elara in 1905, Pasiphaë in 1908, Sinope in 1914, Lysithea and Carme in 1938, Ananke in 1951, and Leda in 1974. By the time Voyager space probes reached Jupiter around 1979, 13 moons had been discovered; while Themisto was observed in 1975, but due to insufficient initial observation data, it was lost until 2000. The Voyager missions discovered an additional three inner moons in 1979: Metis, Adrastea, and Thebe.

For two decades no additional moons were discovered; but between October 1999 and February 2003, researchers using sensitive ground-based detectors found another 32 moons, most of which were discovered by a team led by Scott S. Sheppard and David C. Jewitt. These are tiny moons, in long, eccentric, generally retrograde orbits, and average of 3 km (1.9 mi) in diameter, with the largest being just 9 km (5.6 mi) across. All of these moons are thought to be captured asteroidal or perhaps cometary bodies, possibly fragmented into several pieces, but very little is actually known about them. A number of 14 additional moons were discovered since then, but not yet confirmed, bringing the total number of observed moons of Jupiter at 63. As of 2008, this is the most of any planet in the Solar System, but additional undiscovered, tiny moons may exist.